From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomasz Chmielewski Subject: Re: strange guest slowness after some time Date: Tue, 17 Mar 2009 19:55:09 +0100 Message-ID: <49BFF20D.6010303@wpkg.org> References: <49B29705.6000904@wpkg.org> <49B4E7A6.3090601@redhat.com> <49B4EDC9.9020504@wpkg.org> <49B4EE8F.7050001@redhat.com> <49BD007C.9030809@wpkg.org> <49BF7FB6.9080503@wpkg.org> <49BF8686.5050707@redhat.com> <49BF88BE.7040805@wpkg.org> <49BFC276.1080600@gmx.net> <49BFC743.20000@redhat.com> <49BFCC04.9080402@wpkg.org> <49BFD84F.8050509@gmx.net> <49BFD999.503@redhat.com> <49BFE146.2090308@wpkg.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Felix Leimbach , kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mx03.syneticon.net ([78.111.66.105]:45699 "EHLO mx03.syneticon.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754809AbZCQSzR (ORCPT ); Tue, 17 Mar 2009 14:55:17 -0400 In-Reply-To: <49BFE146.2090308@wpkg.org> Sender: kvm-owner@vger.kernel.org List-ID: Tomasz Chmielewski schrieb: > Avi Kivity schrieb: >> Felix Leimbach wrote: >>> Tomasz Chmielewski wrote: >>>> Avi Kivity schrieb: >>>>> Might it be that some counter overflowed? What are the packet >>>>> counts on long running guests? > >>> Here is the current ifconfig output of a machine which suffered the >>> problem before: >>> >>> eth0 Link encap:Ethernet HWaddr 52:54:00:74:01:01 >>> inet addr:10.75.13.1 Bcast:10.75.255.255 Mask:255.255.0.0 >>> UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 >>> RX packets:3542104 errors:0 dropped:0 overruns:0 frame:0 >>> TX packets:412546 errors:0 dropped:0 overruns:0 carrier:0 >>> collisions:0 txqueuelen:1000 >>> RX bytes:682285568 (650.6 MiB) TX bytes:2907586796 (2.7 GiB) >> >> packet counters are will within 32-bit limits. byte counters not so >> interesting. > > Ah OK. > I did only byte overflow. > > Packet overflow will take much longer. It's one of these very rare cases > where setting very small MTU is useful... OK, another bug found. Set your MTU to 100. On two hosts, do: HOST1_MTU1500# dd if=/dev/zero | ssh manager@HOST2 dd of=/dev/null HOST2_MTU100# dd if=/dev/zero | ssh manager@HOST1 dd of=/dev/null HOST2 with MTU 100 will crash after 10-15 minutes (with packet count still not overflown). -- Tomasz Chmielewski http://wpkg.org